Wednesday, September 26, 2012

Potassium permanganate spray is done on jeans to take a bright effect on sand blast area. One important thing about potassium permanganate spray is, this is usually a sporting process to increase the effect of sand blast. Potassium permanganate solution is sprayed on blasted area of jeans garment with the help of normal spray gun. This potassium permanganate spray appears pink on garment when fresh and turns to muddy brown on drying. The garment is hanged in open to dry after potassium permanganate spray and when the potassium permanganate turns its colors completely then it is considered to ready for next process.
It is always followed by neutralization process. Sodium Meta bisulphate is most commonly used neutralizer. A number of products are available in market for neutralization process like sodium meta bisulfate selected on the bases of effect required on blasted area.

Potassium permanganate spray in best is done in specific spray booths, where rubber dummies are installed for holding garments. Garments are mounted on the dummies and air is filled so the garment is full fit exposed. Specific dummies are used for different sizes and styles, like for kids, men’s, trousers, jackets, shirts etc. The booths are fitted with proper air exhaust system. This system leads the spray to treatment room where the chemical mixed air is usually passed through the water showers. Potassium permanganate is dissolved in water and the clean air is blown to open. Shower water is further treated with mild quantities of neutralizer before adding to main drain. But where the potassium permanganate spray is used in low concentrations then there is now need to treat shower water. This mild potassium permanganate mixed water is rather useful for water reservoirs to keep the water clean and germs free.

Potassium permanganate spray concentrations ranges form .25 gm per liter to 15.00 grams per liter depending to required results and fabric types. Usually indigo died fabrics are treated with low concentrations whereas Black Sulfur Fabric requires high concentrations to treat with. Sulfur is not much affected with potassium permanganate and hence requires high concentrations and even sometime multiple spray operations. It is more effective to add potassium permanganate brushing to aid the spray effect. It is very important to equip the operator with gloves, gas mask and gaggles. Long time breathing in potassium permanganate spray may cause health complications so proper preventive measures are to be taken for this department.

Garments are mounted on air filled rubber dummies and chemical is sprayed on blasted areas. The variables in spray process are as follow]

1.    Distance of spray gun to garment- less distance will give more defined and sharp effect where as distant spray will result to more mild and merged effect. Distance ranges form one foot to two and a half foot.

2.    Air to Water Ratio of Gun- this is to be set very carefully. Low air pressure possibly will through KMnO4 drops on garment resulting to bright white spots whereas high pressure will produce very low bright effect spray effect to areas where it is not required.

3.    Potassium Permanganate Solution Concentration- of course, this will control the extent to brightness.

KMnO4 Brushing

In KMnO4 Paint, solution of potassium permanganate is applied to garment with paint brush rather to spray with gun. The effect is quite different to spray as we discussed in last that spray is only to aid the sand blasting effect and is done in addition whereas the potassium permanganate paint is itself a process to give its own effect. The solution of potassium permanganate ranging from 0.10 gm per liter to 5.00 gm per liter is used in normal productions.

In usual, it is done with regular paint brushes or the brushes are modified by cutting hairs in different shapes to produce new styles. Rather towels, sponges, straw bunches or other objects are also used to create effects. What it is seen, is that most merging and beautiful effects are created with towel. Towel dipped in solution are drawn over the garment very lightly. This produces random effect and looks great with dark washes in contrast.

 Courtesy: Denim Help

Wednesday, September 1, 2010

Garment Dyeing - Part-3 - Chemicals and Auxiliary Chmicals - Selection and Analysis

In garment processing we are using a lot of basic chemicals, auxiliary chemicals, enzymes and natural resources such as water. All the above said ingredients play its own important role.

  • Water plays the key role in any textile wet processing. The quality of water decides the quality of your product and rework percentage.  In all climatic condition no water quality would remain same. Rainy season will bring more turbidity and mineral content in running water (river) and more soft and less saline water in bore wells. Providing a good quality water for processing is the basic requirement for any processing unit. How to test and treat water and make it suitable for dyeing is a separate line of discussion.

  • Basic Chemicals: In garment processing we are using the following basic chemicals. The purity of these chemicals is also very important from the point of dyestuff behavior and economy. Some examples are:
      • Common Salt - Common salt is used in reactive, direct and sulphur dyeing processes as a dye exhausting agent. The high impurities present in salt will precipitate on the garment being processed during the addition alkali (soda or caustic) in to the dyeing bath. The unwanted metal ions present in the contaminated salt, like Calcium, Magnesium, Manganese, Iron, Aluminium etc some time replaces the metal ions present in the dyestuff and make the shade appear duller and different in tone. By using a good quality salt like Galuber's salt (Na2SO4) or pure vacuum salt (common salt purified), would save you from these problems. While selecting a basic chemical, buy it from reputed manufacturer and ask them provide you purity certificates. If necessary you can also test the purity of chemicals.
      • Soda Ash - Purity testing of soda ash is very important because the concentration decides the correct pH requirement for fixation of reactive dyes.
      • Hydrogen Peroxide - Hydrogen Peroxide is being sold under two concentrations viz., 35% and 50%. According to the strength the dosage in bleaching varies. Being water like adulteration very easily possible and this decides the batch whiteness. If whiteness between varies, then the final shade also will vary in tone and depth.
      • Acetic Acid - Acetic Acid is used as a neutralizing  agent in two stages of processing, viz., after bleaching and after dyeing. Both stages are very important to achieve the required results. Improper neutralization before dyeing leads to patchy dyeing and after dyeing results in fastness related problems and tonal variations of many shades.
  • Auxiliary Chemicals  - inclusion of too many products for processing leads to loading of effluent and creates complications in treatment. Moreover poor quality products purchased only with the aim to reduce cost of production ends up in many quality problems. If you have a simple analytical lab you can test all auxiliary chemicals at your end itself as a standard practice. We can suggest you the optimum number of essential products for any type of dyeing or finishing.

    Garment Dyeing - Part-2 - Dyestuff Selection - Shade matching

    Different dyes for different colors/effects:

    Selecting Dyes

    There are several different types of dye available for garment dyeing including reactives, pigments, and direct dyes. Dyes are selected based on the fabric (or combination of fabrics) to be dyed, the garment type, and the desired color, consistency, texture, and feel of the finished garments.

    The type of dye selected can also impact the shade range and light fastness of the finished garment. Therefore, it is important to consider the function of the finished garment. For example, light fastness would be an important consideration for summer tanks to be worn in the sun consistently, whereas, light fastness may not be an issue for under garments.

    For your information, following is a table describing some of the factors to be taken into consideration when selecting dye types.

    We would be happy to consult with you when it comes time to dye your garments!

    The table gives fairly a working idea for dyestuff selection. But this is not the final. For example if you opt to select reactive dyes, you still have to make your correct decision which group of reactive dyestuff you have to select.

    There are cold brand (room temperature dyeing), Vinylsulphone, Bifunctional, High Exhaust and so on. Similar is the case with direct and pigment dyes. We have pleasure in advising for proper selection of dyestuff with respect to quality, economy and application ease.

    Garment Dyeing - Part-1 - Check List for PFD garments

    Well prepared is half dyed! - this is a dyers' slogan.

    Quality Assurance is a defense mechanism that protects us from flaws and problems that may sprout out after dyeing and finishing. A thorough inspection by qualified people will save a lot. We at Nuchem suggest our clients to make the following tests before starting Garment Dyeing.

    What you need to know before dyeing your garments?:

    •      Some dyeing processes may cause unseen garment flaws to become apparent subsequent to processing; such as pin holes, bad seams, and optical spots. As these flaws are inherent in the garments prior to processing, which the dyer cannot be responsible for.
           Because each garment costs more and job dyers are very much responsible for any fault after processing,  a pre-inspection  of greige garments in a dark room equipped with UV lights may proves effective to locate optical brightener spots, oil marks and even sewing thread variations.

    •      Many garments are cut and sewn from previously prepared/finished fabrics (such as water repellants, fire retardants, fluorocarbon, silicone softeners or resins), which may impact the dying process.
           This is a typical case and all garment dyers would regularly face this type of incidents. A better solution is to dye one or two random pieces in a sample garment dyeing machine and get the party's approval.

    •      Many garments are assembled using several different types of fabric. Dye saturation levels and shrinkage may differ between fabric types (even if it is all cotton, as in Greige cotton and bleached cotton combinations) causing unpredictable results.
           As told for the earlier point the only suggestion to  make a sample dyeing and find out the final effect and get the approval of the concerned party.

    •      The garment dyer has no idea in most cases what is present on the garment or how it will behave in the dyeing process. Even on well prepared cloth there will be residual oils, fats, waxes, sizes on woven goods, spinning oils, etc, all of which should be removed to be able to dye successfully.
    •      Also to be taken into consideration is the shrinkage, creases, threads, labels and buttons.
    Open seams, wrong stitching techniques, non- matching threads, and missing stitches, improper creasing of the garment, erroneous thread tension and raw edges are some of the sewing defects which can affect the garment quality adversely. During processing the quality control section needs to check each prepared article against these defects.

    Tuesday, August 31, 2010

    Reductive Bleaching For Denim Garments - Less Rejections & Excellant Softness

    A large part of denim garments are subjected to processes that make them aged or old or worn out. This aged effect is generally obtained by a hypochlorite or peroxide bleaching of the garment or by stone washing or by an enzymatic bleaching treatment with the help of cellulase enzymes. In all the above cases the garment processors land up with the following problems:
    • No uniformity in ageing or fading of shades; generally out of 100 garment pieces about 10 to 15 may got over bleached or under bleached due to the aggressive nature of the bleaching agents used.
    • Generally the bleached garments become very harsh to feel. Every time a a softening treatment is required.
    • If enzymes such as cellulase are used, they have to be deactivated to stop the process at the required stage.
    But all the above said problems can be over come by your own home made Reductive Bleaching Agent.

    How to make an effective Reductive Bleaching Agent?

    What are the chemicals or ingrediant required for making this?

    Its very simple.

    Ingredients and 2  formulas:

    For Making 100 kgs of Reductive Bleaching Agent -1.

    • Liquid Glucose = 850 grams
    • Non-ionic Detergent =  40 grams (100% Ethoxylate Based fatty alcohol poly glycolic ethers)
    • Ammonium Sulphate = 110 grams (You can use Ammonium Chloride, acetate, citrate)
    All mixed together  gives 1kg of Type-1 Reductive Bleaching Agent.

    For Making 100 kgs of Reductive Bleaching Agent -2.

    • Liquid Glucose = 830 grams
    • Non-ionic Detergent =  70 grams (100% Lauric Acid Based n-methy glucomide)
    • Sodium Citrate = 80 grams 
    • Sodium Perborate = 20 grams

    Bleaching Treatment:

    Treat the  the materials to be bleached with sufficient quantity of caustic soda lye so that the pH of the bath is 13 to 14 at 90°C for 15 minutes. To this bath add 0.15% to 0.2% of the above Reductive Bleaching formulation. Continue treatment at 90°C for 80 minutes.

    Drain the bath. Do 1 cycle cold wash followed by mineral acid neutralization. (About 3 to 5 gpl of HCl (35%) may be used for neutralization. Go Cold wash thoroughly to ensure complete removal of mineral acid.Hydro Extract and tumble dry.

    You will get uniformly aged/worn out denim garments with good soft feel.

    (Try these experiments for a very small batch and adjust the recipes according to your actual requirements).

    Wednesday, July 28, 2010

    Heat Sensitive Thermochromic dyes on Garments - a special effect!

    Thermochromic colors:
    Color changing inks were introduced during the 1970s with novelty items such as cups that change color when not liquids such as coffee or tea are poured in to them.
    Color changes of thermo chromic pigments are induced by a temperature change. When temperature rises to a specific temperature, the color changes. The color starts fading back to the original color as the pigment is cooled down. 

    Application of thermo chromic color on garment:
    There are fifteen thermo chromic colors like Americos Red, Magenta, Vermilion, Orange, Yellow, Yellow Green, Charm Green, Sky Blue, Turq Blue, Dark Blue, Violet, and Black. The temperature interval available from 0OC to 70OC. Specific demand can be set up for different temperature intervals from 2OC to 10OC.

    By using the above colors another color can be obtained but use different colors of thermo chromic pigments with the same temperature range to create more colors. Regular pigments can also be mixed with thermo chromic pigment so that the color can be changed from one to another. At lower temperature, the color reveals matched shade. When the temperature is increased, the thermo chromic pigments start fading to colorless. It only shows color of the regular pigments. By mixing the thermo chromic pigments with different temperature ranges, the color can be varied for more than two colors like temperature ranges for 3 color variation.
    These t-shirts and other garments can change color by wearing or touching them. The heat from your body, hand or the environment makes this clothing change color. Once cooled the fabric changes back to the original color.

    Sun Fading dyes and special effect garments

    SUN FADING  - Photochrmic dyes on garments

    Photo chromic color changes from clear when indoors to color when taken out-doors. The phenomenon produced in Photo chromic materials is called photochromism, where the change in color is due to incident light. Specifically, they exhibit color in response to exposure to sunlight or other source of UV radiation. UV light changes the chemical structure of the photo chromic material and makes it absorb color like a dye. It then reverts to a clear state when the UV source is removed.

    However, to date, photochromism is most important for optical switching data and imaging systems, rather than in textile applications.

    Application of photo chromic colors on garment:
    Now  photo chromic colors are plastisol based ready to use off-white liquid are available in the market. When exposed to UV radiation, color appears. These colors are available in various hues.

    Photo chromic colors can be applied on garment by three methods:
    •    Spray
    •    Brush
    •    Screen Print
    In all the above methods, photo chromic colors are directly applied on garment and cured at 1500C for 30-90 seconds.

    These t-shirts and other garments can change color by wearing or touching them. The heat from your body, hand or the environment makes this clothing change color. Once cooled the fabric changes back to the original color.

    The ghost printed  t-shirts have color changing screen prints when exposed to sunlight. The screen print appears as a black and white image with color highlights when indoors but once you go outside into the sun it appears in full color.